Etch the borosilicate glass to form a straight through-glass-via based on the FLACE technology

Interposers will become in demand for advanced electronic systems and through the substrate, vias are essential for 3D integration. A straight via is necessary because a tapered hole is accompanied by large signal loss. This article reports a straight through-glass-via (TGV) fabricated by femtosecond laser-assisted chemical etching (FLACE). The femtosecond laser was used to modify the glass substrates, and the modified glass samples were etched with hydrofluoric acid (HF) solution to form TGV. The effects of key processing parameters, including laser pulse energy, the number of burst pulses, and the HF solution concentration, on the TGV taper profile, were systematically investigated. It was found that The TGV taper sidewall angle decreases with increasing laser pulse energy and increases with increasing HF solution concentration. The number of bursts should be optimized because more than 10 bursts would prevent TGV formation. The study shows via etched in 3 wt% HF after irradiation with 3 bursts of 60 mu J can become approximately vertical. Among the three processing parameters, HF concentration was found to be the most crucial parameter. This work can serve as a critical reference for applications of TGV in high-performance 3D integrated circuits.